What can suprathermal electron tell us about the topology and evolution of CMEs?

Coronal mass ejections (CMEs) undergo multiple evolutionary processes during their propagation through the heliosphere, such us deformation, rotation, and erosion. These processes may result from interactions with the ambient solar wind or with other large-scale structures. However, due to the limitation of single-point measurements of solar wind plasma or interplanetary magnetic field (IMF) properties, it is extremely challenging to infer their topology or evolutionary processes that may have undergone.

Suprathermal electrons are continuously emerging from the solar corona along the IMF. They travel faster than the solar wind, and when comparing their intensity to the direction of the IMF (i.e. analysing their pitch-angle distributions, PADs), we can extract fundamental information about the IMF topology and the conditions of the solar wind plasma. Therefore, understanding the behaviour of suprathermal electron PADs during CME encounters sheds light on the IMF that these particles travelled through, which presumably corresponds to their global structure.

Extracting the information from long periods of observations of suprathermal electron PADs, however, can be challenging. Recently, Carcaboso et al. (2020) introduced a robust method to compute large number of suprathermal electron PADs from distinct missions and derive different properties from their shape. This method can, among others, characterise salient features, automatically identify various PAD types –such as bidirectional, isotropic, simple strahl, loss cone, and pancake–, and quantify the degree of anisotropy.

Recent missions like Parker Solar Probe or Solar Orbiter enable us to observe CMEs at varying heliocentric distances during the ongoing solar cycle (SC25), which is crucial to understand their evolution and topology from the initial stages to more advanced phases. This provides a unique opportunity for a thorough analysis of suprathermal electron PADs at different heliocentric distances, offering insights into how CMEs evolve and interact with the solar wind.

By applying the suprathermal electron PAD analysis method introduced by Carcaboso et al. (2020) to the unique data from the most recent heliospheric missions, this work aims to enhance our understanding of CME evolution and global topology.

 

Carcaboso, F., Gómez-Herrero, R., Lara, F. E., Hidalgo, M. A., Cernuda, I., & Rodríguez-Pacheco, J. (2020). Characterisation of suprathermal electron pitch-angle distributions-Bidirectional and isotropic periods in solar wind. Astronomy & Astrophysics, 635, A79